This invention relates generally to the recovery of raw materials from regenerated cellulose film and more particularly to the recovery of cellulose, softener, and coating resins from softened and coated cellophane scrap and waste.
In the production of regenerated cellulose films such as cellophane, there are a number of stages in the process where waste or scrap materials are produced such as edge trimmings and ends, in addition to downgraded or off-quality film that cannot be used. Recovery of cellulose from such waste cellophane has been a need of the industry for years and processes have been developed to separate the raw materials that make up the film for recycling. However, this is difficult because the cellulose cannot be easily recovered due to the various softeners and coatings applied to the film during its manufacture. Cellophane, produced according to the viscose process, involves converting cellulose pulp to cellulose xanthate which is dissolved in a caustic soda solution to obtain viscose. The viscose is then forced through an elongated orifice as a continuous sheet into a coagulating bath where a coherent web is formed which is subsequently regenerated, washed, desulfured, and bleached. The resulting web is then softened by passng it through a tank containing an aqueous solution of a plasticizer or softener such as ethylene glycol, glycerin, propylene glycol, or urea, and dried to a moisture content of about 4 to 10%. Thereafter a moistureproof coating is applied to both sides of the film. Such moistureproof coatings may be comprised of nitrocellulose or polyvinylidene chloride (saran), depending upon the end use for the film. In some cases, the film is left uncoated for those applications in which moistureproofing is not desired. In any event, during the processing and slitting of the film, trimmed waste and scraps are produced as well as film of inferior quality which cannot be used for its intended purpose.
There are several known processes that have been developed to recover the basic materials from such waste and scrap cellophane. However, none are economically realistic due to the complexity and multiplicity of steps required in order to separate the various components from one another. For example, U.S. Pat. No. 2,337,928 discloses a process for recovering waste material resulting from the manufacture of moistureproof regenerated cellulose film in which the moistureproof coating is first extracted from the film with a solvent mixture of toluene and butyl acetate in order to separately recover the moistureproof composition, then the remaining material is extracted with a solvent for the softening agent in the film to separately recover the softening agent, and then the resulting material is finally treated to recover the cellulose in relatively pure form. Another process is disclosed in U.S. Pat. No. 3,758,457 which, inter alia, involves humidifying comminuted cellulose scrap by adding water in order to swell the cellulose, extracting the water and softener from the humidified comminuted cellulose by flushing it with an extraction agent, drying the coated comminuted cellulose to remove the softener extracting agent, removing the coating from the comminuted cellulose by flushing it with a coating solvent, followed by adding water and more coating solvent to the comminuted cellulose to form a slurry and drying the slurry of water, coating solvent, and comminuted cellulose with a stream of gas to selectively remove the coating solvent leaving dried comminuted cellulose. As is evident, both of these processes are very complex and involve the utilization of two different solvents, one for the softener and the other for the coating resins, in order to recover the cellulose. Also, recovery of the softener from its solvent and the coating resin from its solvent is difficult. From a practical standpoint, none of the prior art processes have proved satisfactory for various reasons, primarily because none are economically feasible. Moreover, they are not readily adaptable to cellophane scrap bearing different coatings or softeners so as to enable the recovery of raw materials from uncoated, nitrocellulose coated, or polyvinylidene chloride coated cellophane, much less the recovery of the various types of softeners that may be used during the production of such film.